Vince Pitelka on tue 21 may 96
Michelle -
There are several significant differences in the two burner configurations you
speak of. The disadvantage to the burners coming into the sidewalls is that
they take up room on either side of the kiln, and you must have a bagwall to
deflect the flames, which takes up kiln space. On the positive side you can
get away with less burners, pilots, baso valves, etc. With the burners coming
up from beneath along the inside wall of the kiln you can eliminate the
bagwall, but there are other concerns. Before every firing you must check very
carefully that nothing has fallen down into the burner-tips, and if a bisque
piece explodes during the firing, pieces can lodge in the burner tip. This is
often not a problem in other than car kilns, because the burner ports are often
beneath the lower shelf and less subject to foreign object blockage. Also,
with such a large number of burners, having individual pilots and baso valves
for every burner is going to be expensive. I would imagine that you would use
those MR-750 venturis which Marc Ward sells, which are very reasonably priced
and work great, but the other components are really going to add up. All the
old natural draft updrafts with a burner array under the floor used to have a
continuous tube-burner or ring-burner with a single pilot and baso. You would
light the pilot, and then turn on the ring burner, which would then light all
the main burners. This system has problems and is no longer considered safe
for institutional use. The state required us to replace these systems on our
natural draft updrafts years ago. The replacement has pilots, thermocouples,
and baso-valves on every burner.
Why not consider a pair of powerburners like the ones Marc Ward sells, mounted
on either side of the chimney. The burner ports would be located in the lower
outer corners of the back wall, so that the flames pass down the side walls of
the kiln towards the front. Some people use a minimal bag wall with this
system, some none at all. Some use a target brick part way down the firebox to
deflect the flame around the kiln. Marc's powerburners come in several
different BTU ratings, and a pair of the lower-rated ones would be more than
enough to fire the size kiln you mention. We have a 50 cu.ft. downdraft with
two such burners and it performs very well.
If it were me I'd just go for the four venturis in four burner ports in the
side walls, with a bagwall. I like natural draft. And I like the way a
bagwall directs the heat upwards, and I like the way that space above the
firebox and bagwall allows the heat and atmosphere to circulate. I guess I'm
pretty conservative in this regard. A bagwall on each side, built of bricks on
edge or end is only an additional five inches overall in the width of the kiln.
- Vince
Vince Pitelka - wkp0067@tntech.edu
Appalachian Center for Crafts - Tennessee Technological University
Smithville, TN
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